1. Field of the Invention
The present invention relates to an electric clamp apparatus which makes it possible to clamp a workpiece to be positioned on a carriage and transported, for example, in an automatic assembling line.
2. Description of the Related Art
Conventionally, for example, in an automatic assembling line for automobiles, a workpiece such as an engine is transported by using a carriage, and it is subjected to a variety of machining steps and assembling steps at respective stations.
In each of the stations, it is necessary to position the workpiece at a predetermined position in order to fix the workpiece to a jig. In recent years, a system is adopted, in which a clamp apparatus is provided for the carriage itself, the workpiece is transported in a state of being clamped on the carriage, and only the carriage is positioned in each of the stations.
In this system, a fluid pressure-operated cylinder, for example, a pneumatic cylinder is used as a driving source for driving the clamp apparatus.
However, the clamp concerning the conventional technique as described above involves the following inconvenience. That is, for example, when the pneumatic cylinder is used as the driving source, then the air piping is required, and the piping operation is complicated. Further, the installation space is restricted due to a plurality of tubes to be used for the air piping.
Further, it is necessary to install, for example, a fluid pressure-operated apparatus (for example, pressure reducing valve) for controlling the supply pressure so that the pressure (source pressure) of the compressed air supplied from a compressed air supply source is adapted to the pneumatic cylinder to be used. An inconvenience arises such that it is impossible to contemplate effective utilization of the installation space.
Furthermore, it is demanded to enhance the clamping force on the workpiece by further increasing the driving force of the driving source.
In view of the above, as shown in FIG. 8, a toggle lever-tightening apparatus 3 is suggested, in which the rotary motion of a motor 1 is converted into the rectilinear motion of a screw spindle 2, and thus the screw spindle 2 is displaced in the upward and downward directions (see the specification of European Patent Publication No. 0243599A).
The toggle lever-tightening apparatus 3 concerning the conventional technique adopts the following arrangement. That is, the motor 1 drives a pinion 5 by the aid of a drive shaft 4, the pinion 5 is meshed with a gear 7 having teeth 6 at the inner side, and the teeth 6 are cooperated with the screw spindle 2. The screw spindle 2 is displaced in the upward and downward directions depending on the direction of rotation of the motor 1.
However, the toggle lever-tightening apparatus 3 concerning the conventional technique described above adopts the arrangement in which the rotary driving force of the motor 3 is directly transmitted to the screw spindle 2 by the aid of the gear 7. In the case of the gear 7 which is formed to have a thin-walled wall thickness, the meshing portion with respect to the screw spindle 2 is designed to be small. It is feared that the durability is deteriorated by the load exerted on the meshing portion, and hence any fluctuation occurs in the rectilinear motion of the screw spindle 2.
Further, the toggle lever-tightening apparatus 3 concerning the conventional technique described above involves the following inconvenience. That is, the large shock arises at the displacement terminal position of the rotation of the arm 8. The vibration, which is caused by the shock, is transmitted to the meshing portion between the screw spindle 2 and the gear 7 and to the meshing portion between the pinion 5 and the gear 7 respectively. As a result, the smooth rectilinear motion of the spindle 2 is obstructed. Further, the durability is deteriorated for the members (screw spindle 2, gear 7, and pinion 5) for constructing the meshing portions.
A general object of the present invention is to provide an electric clamp apparatus which makes it possible to eliminate the complicated air piping or the like, and effectively utilize the installation space.
A principal object of the present invention is to provide an electric clamp apparatus which makes it possible to further increase the clamping force by using, as a driving source, a rotary driving source which performs rotary driving in accordance with an electric signal.
Another object of the present invention is to provide an electric clamp apparatus which makes it possible to avoid the transmission of the vibration caused by the shock, to a gear mechanism or the like in a body, by buffering the shock which is brought about when a clamp arm arrives at the displacement terminal position.
Still another object of the present invention is to provide an electric clamp apparatus which makes it possible to smoothly displace, in the linear direction, a ball screw shaft to which the rotary driving force of a rotary driving source is transmitted.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.